U.S. patent number 9,738,040 [Application Number 14/530,465] was granted by the patent office on 2017-08-22 for method of making a spectacle lens.
This patent grant is currently assigned to Carl Zeiss Vision International GmbH. The grantee listed for this patent is Carl Zeiss Vision International GmbH. Invention is credited to Stephan Duewel, Norbert Kurz, Ralf Meschenmoser, Malte Riedel.
United States Patent |
9,738,040 |
Meschenmoser , et
al. |
August 22, 2017 |
Method of making a spectacle lens
Abstract
A method for making a spectacle lens includes joining a mold and
a sealing ring. The mold has an integrated block piece and a mold
shell made by primary shaping and the sealing ring has a first end
face, a second end face, a peripheral seal, an opening disposed on
the first end face configured to receive a mold, and a flexible
membrane on the second end face. A polymerizable material is
introduced into the mold cavity with the aid of a pump action of
the flexible membrane of the sealing ring. The flexible membrane of
the sealing ring is fixed in a desired surface shape and the
polymerization is carried out. The mold is removed with a cast-on
spectacle lens blank.
Inventors: |
Meschenmoser; Ralf (Essingen,
DE), Kurz; Norbert (Aalen, DE), Riedel;
Malte (Aalen, DE), Duewel; Stephan (Aalen,
DE) |
Applicant: |
Name |
City |
State |
Country |
Type |
Carl Zeiss Vision International GmbH |
Aalen |
N/A |
DE |
|
|
Assignee: |
Carl Zeiss Vision International
GmbH (Aalen, DE)
|
Family
ID: |
51862137 |
Appl.
No.: |
14/530,465 |
Filed: |
October 31, 2014 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20150115486 A1 |
Apr 30, 2015 |
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Foreign Application Priority Data
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Oct 31, 2013 [DE] |
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10 2013 222 232 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C
45/376 (20130101); B29D 11/00009 (20130101); B29D
11/00548 (20130101); B29C 45/0055 (20130101); B29D
11/00538 (20130101); B29C 45/37 (20130101); B29L
2011/0016 (20130101) |
Current International
Class: |
B29D
11/00 (20060101); B29C 45/00 (20060101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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10 2009 004 377 |
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Jul 2010 |
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DE |
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10 2009 004 379 |
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Jul 2010 |
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DE |
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2011/110300 |
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Sep 2011 |
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WO |
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WO 2011/110300 |
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Sep 2011 |
|
WO |
|
Primary Examiner: Vargot; Mathieu
Attorney, Agent or Firm: Walter Ottesen, P.A.
Claims
What is claimed is:
1. A method for making a spectacle lens, the method comprising the
steps of: joining a mold and a sealing ring, the mold having an
integrated block piece and a mold shell made by primary shaping and
the sealing ring having a first end face, a second end face, a
peripheral seal, an opening disposed on the first end face
configured to receive a mold, and a flexible membrane on the second
end face with the sealing ring and the mold shell conjointly
defining a mold cavity; introducing a polymerizable material into
the mold cavity with the aid of a pump action of the flexible
membrane of the sealing ring; fixing the flexible membrane of the
sealing ring in a desired surface shape; carrying out the
polymerization in the mold cavity; and, removing the mold with a
cast-on spectacle lens blank.
2. The method of claim 1 further comprising the step of performing
finishing steps for making a finished spectacle lens.
3. The method of claim 1 further comprising the step of performing
prescription grinding for making a finished spectacle lens.
4. The method of claim 1, wherein said fixing the flexible membrane
of the sealing ring in a desired surface shape is done via a
shaping-inputting element.
5. The method of claim 4, wherein said shaping-inputting element is
a spring tension element.
6. The method of claim 1 further comprising the step of performing
finishing steps, at least partially, while the spectacle lens blank
remains in the mold and while using the integrated block piece.
7. The method of claim 2, wherein the spectacle lens blank is made
with a surface allowance of at most 10 mm.
8. The method of claim 1, wherein the spectacle lens blank is made
with a surface allowance lying in a range of 0.2 to 5 mm.
9. The method of claim 2, wherein said performing finishing steps
results in a material removal of at most 20%.
10. The method of claim 1, wherein the mold shell is formed by
injection molding or 3D printing.
11. The method of claim 2, wherein the sealing ring has at least an
inlet channel and an outlet channel for casting compositions in the
region of the peripheral seal.
12. The method of claim 11, wherein the inlet/outlet channels can
be squeezed shut.
13. The method of claim 11, wherein the method step of introducing
a polymerizable material into the mold cavity includes: inserting
the arrangement of the mold and the sealing ring into a pump
mechanism via which the flexible membrane can be subjected to at
least one of underpressure and overpressure; pumping out the mold
cavity so as to remove air; filling the mold cavity with monomer by
generating underpressure via the pump mechanism and stretching the
flexible membrane; and, closing the outlet channel and the inlet
channel.
14. The method of claim 11, wherein the method step of introducing
a polymerizable material into the mold cavity includes: inserting
the arrangement of the mold and the sealing ring into a pump
mechanism via which the flexible membrane can be subjected to at
least one of underpressure and overpressure; pumping out the mold
cavity so as to remove air; filling the mold cavity with monomer by
generating underpressure via the pump mechanism and stretching the
flexible membrane; pressing out excess monomer and, if required,
any air bubbles still present; and, closing the outlet channel and
the inlet channel.
15. The method of claim 1, wherein the sealing ring is configured
to receive a mold in different positions in such a manner that mold
cavities having different edge heights are generated.
16. The method of claim 1, wherein the sealing ring has, on the
inner circumference of the peripheral seal, an arrangement for
fixing a mold in at least one defined depth dimension.
17. A method for making a spectacle lens, the method comprising the
steps of: joining a mold and a sealing ring, the mold having an
integrated block piece and a mold shell made by primary shaping and
the sealing ring having a first end face, a second end face, a
peripheral seal, an opening disposed on the first end face
configured to receive a mold, and a flexible membrane on the second
end face with the sealing ring and the mold shell conjointly
defining a mold cavity; introducing a polymerizable material into
the mold cavity with the aid of a pump action of the flexible
membrane of the sealing ring; fixing the flexible membrane of the
sealing ring in a desired surface shape; carrying out the
polymerization in the mold cavity; removing the mold with a cast-on
spectacle lens blank; and, wherein the spectacle lens blank is made
with a surface allowance of at most 10 mm.
18. A method for making a spectacle lens, the method comprising the
steps of: joining a mold and a sealing ring, the mold having an
integrated block piece and a mold shell made by primary shaping and
the sealing ring having a first end face, a second end face, a
peripheral seal, an opening disposed on the first end face
configured to receive a mold, and a flexible membrane on the second
end face with the sealing ring and the mold shell conjointly
defining a mold cavity and wherein the sealing ring has at least an
inlet channel and an outlet channel for casting compositions in the
region of the peripheral seal; introducing a polymerizable material
into the mold cavity with the aid of a pump action of the flexible
membrane of the sealing ring by: (i) inserting the arrangement of
the mold and the sealing ring into a pump mechanism via which the
flexible membrane can be subjected to at least one of underpressure
and overpressure; and, (ii) pumping out the mold cavity so as to
remove air; fixing the flexible membrane of the sealing ring in a
desired surface shape; carrying out the polymerization in the mold
cavity; removing the mold with a cast-on spectacle lens blank;
filling the mold cavity with monomer by generating underpressure
via the pump mechanism and stretching the flexible membrane;
pressing out excess monomer and, if required, any air bubbles still
present; and, closing the outlet channel and the inlet channel.
Description
CROSS REFERENCE TO RELATED APPLICATION
This application claims priority of German patent application no.
10 2013 222 232.7, filed Oct. 31, 2013, the entire content of which
is incorporated herein by reference.
FIELD OF THE INVENTION
The invention relates to a mold for producing a spectacle lens,
with an integrated block piece and a mold shell. The invention
further relates to a sealing ring for such a mold, an arrangement
made of a mold according to the invention and to a sealing ring
according to the invention, a method for producing a mold according
to the invention, and a method for producing spectacle lenses.
BACKGROUND OF THE INVENTION
In the production of a spectacle lens, a blank is generally first
of all cast from a suitable plastic and, in a second manufacturing
step called the prescription lens manufacture, is brought to the
final shape to achieve the prescription values. The prescription
lens manufacture involves work to remove material. To minimize the
necessary stock of blanks, these blanks are generally made
available only in rough gradations as regards diameter and
curvature of the front and back surfaces. Therefore, in the
prescription lens manufacture, it is generally necessary to remove
a considerable amount of material, usually with about 70% by weight
of the material of the blank being removed and discarded. Recycling
of this material is not possible.
To machine the blank in the prescription lens manufacture, a block
piece has to be attached to the blank, via which the blank can be
retained for working in a suitable machine tool. To mount the blank
on the block piece, a low-melting metal alloy is generally used.
Only a small surface area of the blank is generally blocked, since
the heavy-metal alloys used are very expensive and, what is more,
very elaborate cleaning of the waste water is necessary in order to
avoid contamination thereof with heavy metals. During the
machining, the protruding lens edges tend to experience undesired
oscillations or to yield and fracture. The oscillation can result
in a surface having an undesired structure, and the latter cannot
be polished out, since oscillation and yielding of the lens edge
also occur during the polishing. Moreover, the outer area is
pressed downward during the machining and snaps back again after
the loading, as a result of which a kind of bead can form on the
unmachined back surface.
It has already been proposed (WO 2011/110300 A2), in a conventional
mold, to provide a mold shell with an integrated block piece. After
the casting, the blank remains adhering with a surface (the front
surface or back surface) to this mold shell and, by means of the
integrated block piece, can be machined in the prescription lens
manufacture (on the opposite surface).
United States patent application publication 2011/0018150 A1
discloses a method for producing a spectacle lens, in which method
the as yet unpolymerized resin is introduced into a mold, the front
and rear faces of which are flexible and transparent. The document
proposes that the as yet uncured resin is shaped, in front of the
eye of the future wearer of the spectacles, via the flexible faces,
such that a lens with the desired correction values is obtained. It
appears doubtful whether such a method is practicable.
United States patent application publication 2009/0179339 discloses
a mold and a sealing ring for producing a spectacle lens.
SUMMARY OF THE INVENTION
It is an object of the invention to simply and inexpensively
produce spectacle lenses that are individually adapted to a
spectacles wearer.
According to a first aspect of the invention, this object is
achieved by a method for producing a spectacle lens, characterized
by the following steps: a) joining together i. a mold (1) with an
integrated block piece (13) and a mold shell (11) produced by
primary shaping, ii. and a sealing ring, which has a peripheral
seal (21), on a first side an opening for receiving a mold, and on
the second side a flexible membrane (22), to form a mold cavity, b)
introducing a polymerizable material into the mold cavity (3) with
the aid of a pump action of the flexible membrane (22) of the
sealing ring (2), c) fixing the flexible membrane (22) of the
sealing ring (2) in the desired surface shape, d) carrying out the
polymerization, e) removing the mold (1), with the cast-on
spectacle lens blank, from the sealing ring (2).
Optionally, any necessary finishing steps, in particular
prescription grinding, can additionally be carried out for
producing the finished spectacle lens.
Suitable materials for the sealing ring and flexible membrane are
rubbers and polymers, for example.
Some terms used in the context of the invention will be explained
first of all.
A mold is used to cast at least one surface (front or back surface)
of a spectacle lens from a polymerizable material (monomer). It has
a mold shell (generally either a front or back surface mold shell),
which has a so-called optical surface. The optical surface is the
mating surface for the front or back surface of the blank cast in
such a mold.
The mold has an integrated block piece. Integrated means that it is
connected (preferably integrally) to the mold. The block piece
serves for the temporary connection of the mold (with the casting
(or blank) adhering thereto) to a machine tool.
According to the invention, the mold shell is produced by primary
shaping. This means that at least the area of the mold forming the
optical surface (mating surface for the cast surface) is produced
by material build-up via primary shaping.
According to DIN 8580, primary shaping designates all manufacturing
methods in which a solid body is produced from a formless
substance. The shape of a geometrically defined, solid body is thus
produced and the substance is held together. The starting materials
used can be liquid, plastic, granular or powdery.
A preferred subgroup of primary shaping within the context of the
invention is injection molding. In this method, a polymer
(generally in the form of granules) is plasticized and injected
into an injection molding tool. The cavity of the latter defines
the shape and surface structure of the finished part.
It is likewise possible, within the context of the invention, to
carry out 3D printing as a variant of the primary shaping. 3D
printing is an additive production method in which the desired
shape is produced exclusively by application of material. A
preferred 3D printing method is fused deposition modelling (FDM),
in which preferably a thermoplastic material is applied from a
nozzle in a string shape in order to form the desired structure.
Suitable thermoplastics may be ABS, PC, PLA, HDPE and PPSU, for
example. Since the mold is preferably used as a disposable mold for
producing just a single spectacle lens, biodegradable plastics can
preferably be used. It is likewise possible, within the context of
the invention, for 3D printing to be carried out using
photopolymerizable plastics, in particular UV-curable plastics.
The spectacle lens is produced by casting. To form a mold cavity,
the mold cooperates with a sealing ring.
Together with the mold, the sealing ring forms a mold cavity into
which polymerizable material is introduced for the production of a
blank. This can be a known polymerizable material used for the
production of spectacle lenses, for example CR-39.RTM. (polyallyl
diglycol carbonate (PDAC)), CR-607.RTM. and Trivex.RTM.
(nitrogen-modified polyurethane) from PPG Industries and also the
MR series (thiourethane polymers) from Mitsui Chemicals. Suitable
polymerizable compositions are familiar to a person skilled in the
art.
The flexible membrane of the sealing ring is fixed in the desired
surface shape and the polymerization is carried out. The mold, with
the cast-on blank, is removed from the sealing ring. Any necessary
finishing work is then carried out, in particular prescription
machining (prescription grinding) for the production of the
finished spectacle lens.
The introduction of the polymerizable material into the mold cavity
is effected with the aid of the pump action of the flexible
membrane of the sealing ring. The flexible membrane of the sealing
ring is fixed in the desired surface shape preferably by a shaping
element, more preferably a spring clamp element. Any necessary
finishing steps are preferably at least partially carried out, with
the spectacle lens blank remaining on the mold, using the
integrated block piece.
Preferably, the blank is produced with a surface allowance of 10 mm
or less, more preferably 5 mm or less, more preferably 0.2 to 5 mm.
According to the invention, the material removed in the finishing
work can be small, amounting preferably to 20% by weight or less,
more preferably 10% by weight or less.
The peripheral seal forms the edge areas of the mold cavity and is
therefore circular in order to cast a circular blank. The
peripheral seal cooperates sealingly with the edges of the mold;
here, sealingly means that the leaktightness is sufficient to
prevent escape of polymerizable material from the mold cavity. The
peripheral seal can be made flexible, in such a way that it is able
to cooperate with differently shaped molds. These do not
necessarily have to be circular; instead, their edge can be adapted
from the outset to the desired final shape of the spectacle
lens.
On one face, the sealing ring has an opening for receiving a mold.
It is generally completely open on this face, such that the
peripheral seal sealingly encloses the edge of an inserted mold. It
has a flexible membrane on the second face. This flexible membrane
forms the limit of the mold cavity on this face.
The mold, with a mold shell individually shaped by 3D printing,
permits the casting of a spectacle lens blank with a finished and
individually adapted front surface or back surface. Further working
of the blank, in particular the prescription grinding on the
opposite surface, can take place using the mold as block piece.
During the entire manufacture of the spectacle lens, the cast
finished surface therefore remains protected, and subsequent
application of a block piece for the prescription grinding is
dispensed with. The whole of the cast surface is completely
protected all the way through the manufacturing process.
After the casting process, cast blanks have to be tempered without
stress in the course of cooling. In the prior art, this is
generally done by mounting the semifinished products on lens
plates, with the concave surface facing downwards. During the
tempering, deformations can occur at the elevated temperature. By
contrast, according to the invention, the tempering of the blank
can take place with the mold still blocked. The blank is fully
supported, and deformation cannot take place.
By virtue of the individual manufacture and the one-off use of a
mold produced by 3D printing, it is possible for the cast surface
to be adapted from the outset to the individual requirements of a
spectacles wearer. This entails several aspects and advantages.
In the prior art, the molds are generally used a number of times,
such that individualization of the cast surfaces is not possible
or, at best, is possible to a very limited extent. This means that
a considerable loss of material of 70% or more generally occurs in
the subsequent prescription manufacture. An individually produced
mold can be adapted from the outset to the future spectacles wearer
in terms of diameter, edge shape, the form of the cast surface and
the thickness of the blank, such that only a small amount of
material is removed in the subsequent machining (prescription
grinding).
The surface cast using the mold can be the back surface or
preferably the front surface of a spectacle lens. It can in
particular be made concave or convex and can have single-vision or
multifocal power. The surface can, for example, be spherical,
aspherical, toric, atoric, bifocal, trifocal or can be designed as
a progressive surface.
The mold shell and optical surface of the mold can in particular be
designed for casting a finished spectacle lens surface, it being
possible for the latter to be a prescription surface which includes
some or all of the prescription powers provided for the spectacles
wearer. For example, if a front surface with a progressive power is
cast, this can in principle be a standard progressive surface
without adaptation to an individual user. However, in the context
of the invention, it is preferable if such a progressive surface is
designed as an individual progressive surface in which the
progressive power and/or the arrangement and profile of the
intermediate corridor are adapted from the outset to the intended
spectacles wearer.
A further advantage of the invention is the possibility of
providing the cast surface of the spectacle lens with different
coatings in the course of the casting process. For this purpose,
wet chemical coatings are preferably applied to the optical surface
of the mold shell, which coatings are transferred to the
corresponding spectacle lens surface during casting. The
application of wet chemical coatings to the optical surface can
preferably be done by suitable techniques, for example spin coating
technology. For example, such coatings can have the following
functions, which are listed from the outside inwards (from the
point of view of the finished spectacle lens): anti-fog layer (for
example, nanoparticles) anti-static coating hydrophobic layer
anti-reflective coating polarization layer photochromic layer
adhesive for improving adhesion to the material of the spectacle
lens.
The sealing ring cooperates with a mold to form a mold cavity.
Therefore, in contrast to the prior art, the invention requires
only one mold, of which the optical surface is used to cast a
spectacle lens surface. According to the invention, the opposite
surface of the spectacle lens is cast using the flexible membrane
of the sealing ring as a shaping element.
The shaping element provided for the flexible membrane of the
sealing ring is preferably configured as a spring clamp element.
With this shaping element, the membrane can be brought to the
desired basic shape (generally convex or concave). The shaping, for
example by a spring clamp element, is sufficiently precise to
ensure that only a small material allowance of preferably between
0.2 and 5 mm is present over the form of the intended final surface
(generally a prescription surface), which material allowance still
has to be removed in the course of the prescription
manufacture.
The shaping element is preferably elastic, for example a spring
clamp element, such that changes in volume that take place during
the polymerization, in particular shrinkage, can be automatically
compensated during the polymerization.
The surface of the spectacle lens shaped by the flexible membrane
generally has to be reworked in the context of the prescription
manufacture, in order to achieve the desired prescription powers.
However, as has been described above, at least some of the desired
prescription powers can be obtained by way of the optical surface
of the mold shaped individually by 3D printing.
The sealing ring preferably has, in the area of the peripheral
seal, at least two inlet/outlet channels for casting composition.
These inlet/outlet channels are preferably arranged pointing
radially outwards on the circumference, more preferably lying more
or less diametrically opposite each other, and they are more
preferably arranged closely adjacent to that edge area of the
circumference that faces towards the flexible membrane.
During the casting of a spectacle lens blank, the liquid resin has
to be introduced into the mold. Since air bubbles present in the
resin have a tendency to adhere to inside walls of the mold, in
particular to walls of the sealing ring, it is difficult to fully
displace the air and, in particular, to ensure no air inclusions in
the edge area. In the described aspect of the invention, at least
two channels are present, such that filling can take place through
one channel while the enclosed air escapes through the second
channel. This makes it much easier to fill the mold in a manner
free of bubbles. Of particular advantage in this context is the
flexible membrane of the sealing ring, which serves as a pump
element for the filling process. For example, if the membrane is
moved axially away from the mold via an underpressure, this has the
effect of sucking in casting composition. If, after this
suctioning, the membrane is moved axially back in the opposite
direction, for example by an overpressure, excess casting
composition and any air bubbles that are present are forced out.
The inlet/outlet channels can preferably be made flexible and, as a
result, can be clamped or pressed shut. After the arrangement made
of mold and sealing ring has been filled, this allows the mold
cavity to be easily closed prior to the polymerization.
It is of particular advantage that, according to the invention, the
inlet/outlet channels can be made to take up very little space and
need only little room in the axial direction. According to the
invention, an arrangement composed of mold and sealing ring can be
used to cast lenses with very thin edge heights (these are needed
in particular in plus-power lenses), where only a very small amount
of material has to be removed in the course of the subsequent
machining. According to the invention, it is possible, for example
in any lens shapes, that is, including the described plus-power
lenses with low edge heights, to provide the surface of the
spectacle lens cast by the flexible membrane with only a very small
surface allowance, which can lie between 0.2 and 5 mm, for example.
Values of 0.2-3 mm, more preferably 0.2-1.5 mm, more preferably
0.2-1 mm are preferred. Accordingly, in the subsequent prescription
manufacture, only a very small amount of material is removed. A
particular advantage of the invention is also that, after the
casting, very thin blanks can be tempered free of stress and
without deformations, since during this process they are still
supported by the mold across their whole surface. By contrast, in
the prior art, in which the lenses are generally mounted only on
the edge of the concave surface for stress-free tempering,
undesired deformations increasingly occur specifically in thin
lenses, which deformations often have to be corrected again, at
some cost, by further machining during the prescription
manufacture.
The sealing ring can be designed to receive a mold in different
positions, in such a way that mold cavities with different edge
heights are obtained. The mold can, for example, be inserted to
different depths into the peripheral seal. An arrangement composed
of mold and sealing ring can thus be used variably for different
edge heights of blanks, preferably for example for edge heights of
1 to 20 mm. According to the invention, the mean thicknesses of
lenses can thus likewise be varied in a simple way, with preferred
mean thicknesses lying, for example, between 1 and 20 mm. The
possibility, according to the invention, of casting lenses with
small mean thicknesses permits the manufacture of strong
minus-power lenses, which have very little surface allowance and
accordingly require little material to be removed in subsequent
working.
Provision can be made that a sealing ring has, on the inner
circumference of the peripheral seal, means for fixing a mold in at
least one defined depth dimension. For example, these means can be
in the form of a step on the inner circumference, on which step the
edge of the mold abuts, thereby bringing mold and sealing ring into
a defined axial position relative to each other. If appropriate, it
is also possible for several steps to be provided on the inner
circumference, in order to permit fixing with different depth
dimensions. The sealing ring can additionally have an insertion
bevel, in order to make joining to a mold easier.
According to the invention, blanks can be produced individually in
a broad range of dimensions and curvatures. For example, the base
curves of the cast surfaces can be plane or curved (preferably
convex) with radii of preferably up to 30 mm. If blanks with a
circular circumferential shape are initially to be produced, the
diameters according to the invention can lie, for example, between
40 and 100 mm. Reasonable and sufficiently small gradations of the
diameter can be provided, such that the final spectacle lens can be
produced expediently and with a small amount of material being
removed at the edge. The gradations in diameter can be 5 mm, for
example, while reasonable diameter steps can be, for example, 58,
63, 68, 73 and 78 mm, etc.
In the production of a mold, the surface design of the mold shell
can be established in a first step. Although this can be a standard
design, it is preferably an at least partially individually adapted
design, where the individually adapted aspects can be, for example,
the diameter or shape of the lens, the curvature of the cast
surface, or individual prescription values such as, for example, a
progressive surface with predefined progressive value and profile
of the intermediate corridor. The surface design thereby
established is transferred to a 3D printer. In the next step, at
least the mold shell with its optical surface, or preferably the
entire mold, is produced by 3D printing. To produce this mold,
which is to be used only once, a biodegradable plastic can be used,
which makes it easier to dispose of the mold after it has been
used.
The optical surface of the mold can additionally be polished and/or
provided with at least one wet chemical coating, which is designed
for transfer to the cast surface of the blank or of the casting.
Possible and preferred coatings have already been described above.
A mold can be produced by 3D printing with a lead time of a few
hours and then delivered for the casting process. Since the mold is
preferably used just once, it is possible to avoid the disturbances
on the optical surface of the mold that are customary in multiple
uses (caused, for example, by contaminants or the like in multiple
use).
BRIEF DESCRIPTION OF THE DRAWINGS
The invention will now be described with reference to the drawings
wherein:
FIG. 1 shows an arrangement with a concave mold in cross
section;
FIG. 2 shows the arrangement from FIG. 1 partially filled and with
a membrane fixed by a spring clamp element;
FIG. 3 shows an arrangement with a convex mold in cross
section;
FIG. 4 shows the arrangement from FIG. 3 partially filled and with
a membrane fixed by a spring clamp element; and,
FIGS. 5 to 18 show schematic views of the sequence of a method
according to the invention for casting a spectacle lens.
DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION
FIG. 1 shows, in cross section, a mold 1 inserted into a sealing
ring 2.
The mold 1 has a mold shell 11, which has a mold surface, or
optical surface 12, designed for casting a blank. In the
illustrative embodiment shown, this optical surface 12 is concave;
it can, for example, be a spherical surface or a rotationally
symmetrical aspherical surface.
The mold 1 and in particular the mold shell 11 with the optical
surface 12 are produced by 3D printing. The optical surface 12 has
a shape and surface condition which, during the casting process,
define a surface of a spectacle lens which, without further
working, has a sufficient optical quality. By production by 3D
printing, this surface can in particular be adapted individually to
the intended user and, for example, can already have prescription
values.
The mold 1 has a block piece 13 which serves to connect the mold 1,
and a blank cast thereon, to machining tools for further working of
the blank to give the finished spectacle lens.
The optical surface 12 is provided with wet chemical coatings, as
are described in detail above.
The mold 1 is inserted with its peripheral edge 14 into the
peripheral seal 21 of the sealing ring 2 and is enclosed sealingly
by this peripheral seal 21. The sealing ring 2 has a flexible
membrane 22; in the area of the transition of the flexible membrane
22 into the peripheral seal 21, two inlet/outlet channels (23, 24)
are located at two diametrically opposite positions on the
periphery. The two channels (23, 24) are likewise made from
flexible material and can thus be closed by squeezing them. The
mold 1 can be inserted to different depths into the peripheral seal
21 of the sealing ring 2, in order thereby to cast blanks with
different edge heights. The mold shell 11 and the sealing ring 2
with the peripheral seal 21 and the flexible membrane 22 together
enclose a mold cavity 3.
In order to cast a blank, the mold cavity 3 is filled with monomer
(polymerizable composition). The filling takes place via one of the
channels (23, 24), and the air is preferably allowed to escape from
the mold cavity 3 via the respective other channel. To make filling
easier, the outer face of the flexible membrane 22 is subjected to
underpressure.
After the mold cavity 3 has been filled, the flexible membrane 22
can be brought to the desired shape by a spring clamp element 4
shown in FIG. 2, which shape corresponds approximately to the
desired final shape of the corresponding side of the spectacle lens
plus a surface allowance of 0.2-5 mm. FIG. 2 shows schematically a
state in which the spring clamp element 4 is already fitted and, as
is indicated at 5, the mold cavity 3 is partially filled with
polymerizable composition. It will be noted that this schematically
depicted state does not occur in practice during normal operation,
since the spring clamp element 4 is generally fitted only after
complete filling and evacuation of air from the mold cavity 3.
In the illustrative embodiment of FIGS. 1 and 2, the mold 1, with
its concave optical surface 12, serves for the shaping of a convex
surface of a blank, this generally being the front surface of a
spectacle lens. On account of the individual manufacture of the
mold shell 11 by 3D printing, this front surface does not simply
have to be a standard surface. Instead, it can already be adapted
individually to the user of the spectacle lens. For example, it can
already be an individually adapted progressive surface.
FIGS. 3 and 4 show a second embodiment of the invention. It largely
corresponds to the first embodiment, except that here the mold
shell 11 with the optical surface 12 is made convex in order to
cast a concave surface of a spectacle lens. In this variant, this
is generally the back surface of a spectacle lens.
A particular advantage of the invention is that, also in the mold 1
according to the illustrative embodiment in FIGS. 3 and 4, an
identical sealing ring 2 can be used which interacts with the
corresponding mold 1. As is shown in FIG. 4, the flexible membrane
22 of the sealing ring 2 can be brought by a suitably shaped spring
clamp element 6 to a concave shape pointing towards the mold cavity
3, such that, in the illustrative embodiment of FIGS. 3 and 4, a
convexly shaped spectacle lens is cast on the side of the flexible
membrane 22. In this case also, the spectacle lens surface cast on
the side of the flexible membrane 22 will generally have a surface
allowance of 0.2-5 mm, in order to permit corresponding finishing
in the course of the prescription grinding.
A complete sequence of the method according to the invention for
production of a spectacle lens is described below with reference to
FIGS. 5 to 18.
In the first step, the surface design of the mold is established,
preferably taking account of individual requirements and/or
prescription values. 3D files are derived from the established
surface design and modelled and are transferred to a 3D printer.
The complete mold 1, including the block piece 13 connected
thereto, is produced by 3D printing. It is shown in FIG. 5.
The optical surface 12 of the printed mold can be polished if
required (FIG. 6). It can then be cleaned and, if appropriate,
activated.
The optical surface prepared in this way is preferably coated with
one or more layers applied by wet chemistry (preferably applied via
spin coating technology), as shown in FIG. 7. These layers are
later transferred to the blank during casting.
It is preferable, according to the invention, to precisely measure
the mold surface thus produced and to store the measurement result
in a database. During the subsequent prescription grinding,
recourse can then be made to this measurement result.
The mold that has been produced and prepared in this way is
inserted into a matching sealing ring 2, which is shown in FIG. 8.
Mold and sealing ring are joined axially to the required depth. As
is shown in FIGS. 9 and 10, different depth dimensions can be
chosen in order to cast blanks of different thicknesses.
The inlet and outlet channels (23, 24) of the sealing ring 2 are
connected to the monomer supply (FIG. 11). The thus prepared
arrangement composed of mold and sealing ring is inserted into a
pump mechanism, via which the flexible membrane can be subjected to
underpressure and/or overpressure. The mold cavity 3 is firstly
evacuated by pumping as far as possible, that is, the air is
removed from it (FIG. 12). The mold cavity is then filled with
monomer (FIGS. 12 and 13). The inlet and outlet channels provided
according to the invention easily allow the filling to be carried
out free of bubbles. Via the pump mechanism, sufficient
underpressure can be generated, and the flexible membrane is
correspondingly expanded, such that complete filling without air
bubbles can take place. The outlet channel is closed only when all
the air bubbles are expelled. Thereafter, the inlet channel can
also be closed. The closing can be effected by clamping, as is
indicated schematically at (25, 26) in FIG. 14.
The flexible membrane is fixed in the desired shape via the spring
clamp element 4 being fitted and locked in place (FIG. 14).
According to the invention, the whole procedure can take place
fully automatically in an inline process completely closed off from
the environment, since the simple filling procedure and removal of
air bubbles, made possible according to the invention, permits such
automation.
When filled, the arrangement is detached from the monomer supply
and the polymerization is carried out (FIG. 15). Such a
polymerization cycle can last for up to 48 hours, for example, and
include cooling and heating phases.
After completion of the polymerization, the spring clamp element
and the sealing ring are removed. The blank 27 remains on the mold
according to the invention (FIG. 16), and the corresponding side of
the blank is thus protected in the course of further machining. The
blank is inspected to ensure it is clean.
In the next step, the blank undergoes tempering free of stress
(FIG. 17). During this step, it remains on the mold, which supports
the entire surface of the blank and prevents deformations, even in
the case of blanks that are thin at the edge or in the center. In
the course of further treatment, the mold 1 and the block piece 13
of the mold serve as an interface for holding elements of machine
tools or the like.
In the next step, the surface condition can be examined by suitable
mechanical scanning methods or by reflection methods (for example
the Dual Lensmapper from the company called Automation &
Robotics). The finished blanks, along with the molds remaining on
them, can be packaged and dispatched for prescription grinding.
In the subsequent prescription grinding, the mold serves as block
piece (FIG. 18). After completion of the prescription grinding
carried out in a conventional manner, the finished spectacle lens
is separated from the mold, and the latter is disposed of.
It is understood that the foregoing description is that of the
preferred embodiments of the invention and that various changes and
modifications may be made thereto without departing from the spirit
and scope of the invention as defined in the appended claims.
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